I haven't personally been through with a Libre that I can remember but I have been through with a Guardian CGM sensor multiple times which follow the same guidelines. Usually once I get to the section where the full body scanners are I just let the person know who is stood there that I am unable to go through them as per the guidelines from the company, my last experience weirdly the person at the scanner said it was 'fine' to go through the full x-ray but I was having none of it as that's not what any CGM company suggests is safe and I was adamant they needed to do an alternative screening.
Technically I don't think they can deny you an alternative screening if you ask, each time usually they swab your sensors with a test pad and then they pat you down by hand. I also hand the x-ray technicians where your bags through in the trays a little clear plastic bag with my extra sensors in as a precaution to hand swab those as well instead of sending them through x-ray. You just ask at the end to collect them where you collect the trays with your bags.